1. Technical Field
The present invention relates to an image forming apparatus and a cleaning method therefor, and more particularly, to an image forming apparatus having a charging roll of a contact charging system for charging the surface of an image bearing member, which is driven in rotation, in contact therewith while rotating, and a cleaning member for cleaning the charging roll, and a cleaning method for such an image forming apparatus.
2. Related Art
Heretofore, charging devices such as a scorotron charger that makes use of a corona discharge phenomenon are often used as a charging device of an image forming apparatus such as a copy machine, a printer, and the like that employ an electrophotographic system. In the charging device making use of the corona discharge phenomenon, a problem arises in that ozone and nitrogen oxides, which adversely affect the human bodies and the global environment, are generated thereby. In contrast, the contact charging system, which charges an image bearing member by causing an electrically conductive charging roll to come into direct contact with the image bearing member recently goes mainstream because it greatly reduces generation of ozone and nitride oxides and is excellent in power efficiency.
However, the charging device of the contact charging system has a problem that the surface of the charging roll is liable to be made dirty due to foreign materials deposited thereon because the charging roll is in contact with an image bearing member at all times. The surface of the image bearing member, which repeatedly executes an image forming operation, enters an area of a charging process downstream side of a transferring process after it passes through a cleaning process in which foreign materials such as remaining toner and the like are removed after an image is transferred. However, even if the surface of the image bearing member passes through the cleaning process, a part of toner and particles finer than the toner such as an external additive agent of the toner, and the like remain on the image bearing member without being cleaned and are adhered to the surface of the charging roll. The foreign materials adhered to the surface of the charging roll make the surface resistance value of the charging roll uneven and cause abnormal discharge and unstable discharge, by which charging uniformity is deteriorated.
There is proposed a cleaning system for scraping off the dirt on the surface of the charging roll by abutting a plate-shaped brush and sponge against the surface of the charging roll as a technology for overcoming the above problem. Further, a cleaning system for abutting a roll-shaped cleaning member against the surface of a charging roll is also proposed.
However, the above technologies are defective in that foreign materials gradually deposit on the surface of the cleaning member abutted against the charging roll and a cleaning performance is deteriorated by clogging with a result that the charging roll is made dirty.